Conference Agenda

Hao Chen1, Shuangying Leng1, Jun Huang1, Caroline Jones2, Robert W Williams2, and Burt M Sharp2

Most individuals affected in the national epidemic of oxycodone abuse began taking oral oxycodone by prescription. We studied vulnerability to oxycodone intake in a rat model of oral drug self-administration (SA) under a fixed ratio 5 schedule, where licking was used as the operant behavior. Rats were not water or food deprived. Training started with 0.025 mg/ml oxycodone, gradually increased to 0.1 mg/ml, and session length was extended from 1-h to 16-h, followed by extinction and reinstatement sessions. Females (49 strains) and males (45 strains) licked significantly more on the active spout compared to the inactive spout (p<0.001). The number of active licks were greater in females than males during 4-h and 16-h sessions (p<0.001 for all). Both sexes escalated intake during 16-h extended access vs 4-h sessions (p<2e-16). The heritability of active licks has a range from h2 of 0.22 to 0.59, while that for inactive licks ranged from 0.08, 0.34 at different stages of self-administration. Initial QTL mapping using GEMMA with LOCO identified several significant loci, among them, a region in Chr 1 between 159-172 Mb was associated with oxycodone intake at 0.025, 0.05 and and 0.1 mg/ml, 4h sessions, with max – log10(p) values of 6.1, 5.1 and 5.6, respectively. Potential candidate genes within this range include Cyp2r1 and Pde3b, both have strong cis-eQTL in the brain and are involved in vitamin D metabolism.

1 Department of Pharmacology, Addiction Science And Toxicology

2 Department of Genetics, Genomics and Informatics University of Tennessee Health Science Center, Memphis, TN

Funding provided by NIH/NIDA U01DA053672.

BN Kuhn1 (presenting author underlined)

The rise of opioid use disorder (OUD) worldwide makes it imperative to disentangle the behavioral, genetic and neurobiological correlates associated with both OUD vulnerability and resiliency. Using a novel preclinical rat model of OUD that captures the multi-symptomatic diagnosis and complex multidimensional interactions between symptoms conferring OUD propensity, we have shown distinct behavioral and neurobiological profiles associated with each phenotype (n>1000). Additionally, genome-wide association study (GWAS; n=874) analysis indicates both resiliency and vulnerability to OUD are heritable states. GWAS identified genetic variants for nociception, heroin consumption and motivation to obtain heroin, with OUD vulnerability associated with the latter two. Several of the identified genes are known regulators of neuroplasticity, thereby prompting further investigation into neuroplastic mechanisms contributing to OUD propensity. Guided by findings from GWAS, we are assessing OUD phenotypic differences in components of the extracellular matrix (ECM), microglia and dendritic spine morphology within a canonical circuit necessary for OUD-like behaviors (prelimbic cortex, PrL; nucleus accumbens core, NAc; ventral pallidum, VP). Opposing phenotypic differences in PrL and VP ECM and microglia plasticity are evident, suggesting a mechanistic role for these neuroplastic components in mediating OUD vulnerability and resiliency. Furthermore, cell-specific alterations in NAc dendritic spine morphology are currently underway. Together these data identify novel genetic loci associated with OUD behaviors and vulnerability which further guided the assessment into neuroplastic measures that are likely contributing to OUD vulnerability and resiliency.

¹Department of Psychology and Neuroscience, Baylor University, Waco, TX, USA

Tolulope J Ajanaku^1,2, Eamonn P. Duffy^1,2 , Jonathon O. Ward³, Luanne H. Hale³, Caleb I. Hodges³, Laura M. Saba⁴, Marissa A. Ehringer^1,2, Ryan K. Bachtell^2,3

Prescription opioid use is limited by the development of analgesic tolerance and opioid‑induced hyperalgesia (OIH), yet the extent to which these adaptations are shaped by genetic background versus drug exposure remains unclear. Here, we used 20 inbred Hybrid Rat Diversity Panel (HRDP) strains to quantify strain differences in baseline thermal sensitivity, oxycodone analgesia, the development of tolerance, and OIH following voluntary oxycodone self‑administration. Rats completed a tail immersion test before (Pre‑SA, before self‑administration) and after (Post‑SA, after self‑administration) intravenous oxycodone or saline self‑administration. Analgesia was summarized as the area under the withdrawal‑latency curve, with tolerance defined as the change in area under the curve between trials. Heritability was estimated from the mixed‑effects models of various phenotypes. Baseline and post‑exposure analgesia and thermal sensitivity were moderately heritable (H² ≈ 0.24–0.30), whereas tolerance and change in thermal sensitivity showed much lower heritability (H² ≤ 0.10), indicating a larger contribution of non‑genetic factors to these adaptations. Most strains exhibited classic tolerance to oxycodone, but a few showed sensitization or resistance. Most strains also displayed increased thermal sensitivity after oxycodone self‑administration, indicative of OIH. Surprisingly, total oxycodone intake was only weakly related to tolerance at both individual‑ and strain‑mean levels, suggesting that the mechanisms regulating oxycodone consumption and those governing analgesic tolerance are at least partly dissociable. Together, these findings indicate that opioid analgesia and baseline pain sensitivity are strongly shaped by genetic background, whereas tolerance and OIH that emerge following volitional oxycodone intake are less heritable and loosely related to total drug exposure.

1Department of Integrative Physiology, University of Colorado Boulder, Boulder, CO, USA

2Institute for Behavioral Genetics, University of Colorado Boulder, Boulder, CO, USA

3Department of Psychology and Neuroscience, University of Colorado Boulder, Boulder, CO,

USA

4Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical

Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA

Micah A. Shelton¹, Nicole Horan¹, Xiangning Xue², Lisa Maturin³, Darrell Eacret⁴, Julie Michaud⁵, Navsharan Singh⁶, Benjamin R. Williams⁷, Mackenzie C. Gamble^6,7, Joseph A. Seggio⁵, Madeline Kuppe-Fish⁷, BaDoi N. Phan⁸, George C. Tseng², Julie A. Blendy⁴, Leah C Solberg Woods⁹, Abraham A. Palmer³, Olivier George³, Marianne L. Seney^1*, Ryan W. Logan^7,10*

Opioid use disorder (OUD) has emerged as a severe, ongoing public health emergency. Current, frontline addiction treatment strategies fail to produce lasting abstinence in most users. This underscores the lasting effects of chronic opioid exposure and emphasizes the need to understand the molecular mechanisms of drug seeking and taking, but also how those alterations persist through acute and protracted withdrawal. Here, we used RNA sequencing in post-mortem human tissue from males (n=10) and females (n=10) with OUD and age and sex-matched comparison subjects. We compared molecular alterations in the nucleus accumbens (NAc) and dorsolateral prefrontal cortex (DLPFC) between humans with OUD and rodent models across distinct stages of opioid use and withdrawal (acute and prolonged) using differential gene expression and network-based approaches. We found that the molecular signature in the NAc of females with OUD mirrored effects seen in the NAc of female mice at all stages of exposure. Conversely, males with OUD showed strong overlap in expression profile with rats in acute withdrawal. Co-expression networks involved in post-transcriptional modification of RNA and epigenetic modification of chromatin state. This study provides fundamental insight into the converging molecular pathways altered by opioids across species. Further, this work helps to disentangle which alterations observed in humans with OUD are driven by acute drug exposure and which alterations are consequences of chronic exposure.

¹Department of Psychiatry, University of Pittsburgh School of Medicine
²Department of Biostatistics, University of Pittsburgh
³Department of Psychiatry, University of California, San Diego
⁴Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania
⁵Department of Biology, Bridgewater State University
⁶Department of Pharmacology, Physiology & Biophysics, Boston University School of Medicine
⁷Department of Psychiatry, University of Massachusetts Chan Medical School
⁸Medical Scientist Training Program, University of Pittsburgh School of Medicine
⁹Department of Internal Medicine, Section on Molecular Medicine, Wake Forest University School of Medicine
¹⁰Department of Neurobiology, University of Massachusetts Chan Medical School
*Corresponding authors